Various types of downhole tools are adapted for utilizing an increase in fluid pressure to actuate components of the tool. Packer setting tools, multi-lateral tools and liner hangers are plus exemplary of downhole tools which rely upon an increase in fluid pressure above a seated closure to actuate the tool.
Some tools utilize collet fingers as a ball seat, so that the collet fingers are shifted from the contracted position to an expanded position to allow the ball to drop through the expanded ball seat. Various problems with this design may occur when the collet fingers fail to properly seal and do not allow for pressure to build up so that the collet fingers can move downward and let the ball drop through the seat. Another problem with this type of expandable ball seat is that wellbore fluids pass by the collet fingers, thereby eroding the fingers and tending to cause the ball seat to fail. A ball seat design with collet fingers may also fail to seal properly and not allow for the pressure to build up so that the collets release to pass the ball through the seat. U.S. Pat. Nos. 4,828,037, 4,923,938, and 5,244,044 are examples of patents disclosing expandable ball seats.
U.S. Pat. No. 5,553,672 discloses another design for setting a ball on a seat. This design relies upon a rotating ball valve, so that in one position there is a small hole in the valve which acts as the ball seat. A small ball lands on the small hole, and pressure is applied to the tool. Pressure is applied to rotate the ball, allowing the small ball to drop. This design is complicated with many parts and components that may cause failure.
U.S. Pat. No. 6,681,860 discloses a yieldable ball seat. Quality control for the expandable area may be difficult, and the expandable ball seat may not yield when intended. Material control is also important since the expandable areas expand at a certain pressures. Expandable ball seats thus do not always reliably release the ball at a preselected pressure. In some situations, pressure used to release the ball from the upper seat may generate a full force sufficient to pass the ball through the lower seat, which then makes it impractical to further operate the tool. High pressure applied to the ball releasing system may also damage the tool or damage the skin of the downhole formation.
U.S. Pat. No. 6,866,100 discloses a mechanically expanding ball seat which utilizes pipe manipulation of a drill string after the liner hanger is set to open the seat and release the ball. This system releases the ball mechanically rather than using fluid pressure. The design as disclosed in this patent is complicated, and one has to equalize the pressure across the ball seat before mechanically manipulating the drill string to release the ball.
The disadvantages of the prior art are overcome by the present invention and an improved downhole tool with a C-ring closure seat for receiving a ball or other closure member is hereinafter disclosed.